New insight into knockout reactions from the two-proton halo nucleus ${}^{17}\mathrm{Ne}$

Background: The unexplained disagreement in the dependence of spectroscopic factors $\left(C^2{S}_{\exp }\right)$ on the binding energy obtained by nucleon knockout using different targets is still a puzzle that needs to be addressed.

Purpose: To find an explanation of this riddle through exclusive measurements using different targets.

Method: The exclusive measurements were performed by using a ${}^{17}\mathrm{Ne}$ beam with an energy of 500 MeV/u incident on $\mathrm{C}$ and ${\mathrm{CH}}_2$ targets. Through the standard theoretical approach, $C^2{S}_{\exp }$ were derived from the analysis of the experimental data on proton ejection from the proton halo in ${}^{17}\mathrm{Ne}$ as well as from its core ${}^{15}\mathrm{O}$.

Result: For the $\mathrm{C}$ target, proton ejection from the proton halo gave $C^2{S}_{\exp }$ about 37% smaller than for the $\mathrm{H}$ target. But when protons are ejected from the core of ${}^{17}\mathrm{Ne}$, $C^2{S}_{\exp }$ are identical within statistical uncertainties.

Conclusion: An explanation for the difference in $C^2{S}_{\exp }$ could be the removal of both halo protons, a more important reaction pathway for the $\mathrm{C}$ target. The $C^2{S}_{\exp }$ values obtained by analyzing the proton ejection from the core indicate that it is not affected by the interaction with the halo protons.

Figure 1

Schematic view of the ${\mathrm{R}}^3\mathrm{B}/\mathrm{LAND}$ setup at GSI. The quantities measured with the various detectors of the setup are indicated. DSSD stands for double-sided silicon strip detector, SciFi for scintillation fiber detector and PS PIN for position sensitive pin diodes. For more details, see text.

Figure 2

Energy level diagram for ${}^{16}\mathrm{F}$.

Figure 3

Relative energy spectra $d\sigma /d{E}_{fp}$ obtained in coincidence between ${}^{15}\mathrm{O}$ and a proton ($p_{\mathrm{mult}}=1$) at forward angles after knocking out a proton from ${}^{17}\mathrm{Ne}$ in reactions with the C or H targets. The fits shown are described in the text.

Figure 4

Energy level diagram for ${}^{15}\mathrm{O}$.

Figure 5

Differential cross section $d\sigma /d{E}_{\gamma }$ for the bremsstrahlung $\gamma$ radiation in the beam-at-rest system obtained for $E_{fp}<1.4$ MeV.

Figure 6

Differential cross section in the beam-at-rest system for the detected $\gamma$ rays coincident with ${}^{15}\mathrm{O}+p$ in the final state for $E_{fp}\ge 1.4$ MeV from the C and H targets.

Figure 7

Relative energy spectra of ${}^{15}\mathrm{O}\text{−}p$ in the proton knockout from ${}^{15}\mathrm{O}$ followed by a proton absorption from the proton halo in ${}^{17}\mathrm{Ne}$, leading to the occupation of $\gamma$-decaying states in ${}^{15}\mathrm{O}$, from the C and H targets. The solid lines provide guides to the eye.

Figure 8

Reaction branches accompanying a proton knockout from ${}^{15}\mathrm{O}$, the core of ${}^{17}\mathrm{Ne}$. States weakly populated or unpopulated by proton absorption are shown in red.